The Catholic Church does not use the term "Advent Sunday" of any one Sunday alone. With regard to the Roman Rite, it states that "Advent begins with First Vespers (Evening Prayer I) of the Sunday that falls on or closest to 30 November and it ends before First Vespers (Evening Prayer I) of Christmas", and adds: "The Sundays of this time of year are named the First, Second, Third, and Fourth Sundays of Advent."[2] It also does not allow the use of blue vestments as the liturgical colour of the season. In the Ambrosian Rite and the Mozarabic Rite, the First Sunday in Advent comes two weeks earlier than in the Roman, being on the Sunday after St. Martin's Day (11 November), six weeks before Christmas.[3]

Advent Sunday is the fourth Sunday before Christmas Day. This is equivalent to the Sunday nearest to St. Andrew's Day, 30 November, and the Sunday following the Feast of Christ the King. It can fall on any date between 27 November and 3 December. When Christmas Day is a Monday, Advent Sunday will fall on its latest possible date. Note that it is also possible to compute the date of Advent Sunday by adding three days to the date of the last Thursday of November; it can also be computed as the Sunday before the first Thursday of December.